Considerations for the measurement of very-high-amplitude noise fields

This chapter discusses a research focused on the measurement of very-high-amplitude acoustic noise, primarily jet noise. This research addresses long-range issues in measurement technology in the anticipation of advances in the computational predictions of radiation from full-scale jets. An accurate measurement of acoustic noise very near to the jet plume provides critical data, which are required to validate computational jet-noise models. Different specific sources of jet-engine noise are linked to unsteady flows associated with the mean flow of the engine exhaust. The research intends to develop well-controlled and repeatable sound fields and to measure the perturbation of these fields and the distortion introduced by a number of sensor types and configurations. A technical approach focused to investigate the performance of standard measurement microphones in very-high-amplitude sound fields—with emphasis on the potential degradation of performance because of nonlinear mechanical and acoustical processes—and to develop alternate sensors and sensing techniques against which to compare the performance of standard microphones is also discussed in the chapter.